This invention relates to laminated articles and, more particularly, to composite laminated articles including a bend portion.
In the manufacture of bonded laminated structures, particularly those including woven composite laminae, disposition of the laminae about an out-of-plane angle, for example around the bend of a flange configuration, can result in non-uniform relative movement of the laminae during bonding or curing. Such movement of one laminate over the other can result in wrinkling or delamination of one or more laminae. This is due to differences in bulk shrinkage from the inner portion of the angle or bend to the outer portion, which includes more length or bulk about the bend. The mismatch in outside to inside arc length around the bend tends to manifest itself as out-of-plane wrinkling between laminae generally within or on either side of the mid portion or "knee" of the bend geometry. Several areas of wrinkling or delamination can occur and voids between bonded laminae have been observed. Frequently, such wrinkling is internal and is not evident from external inspection. The existence of such a condition can result in reduced mechanical properties of the article in the bend portion.
In order to reduce or attempt to eliminate such wrinkling, a number of methods and apparatus has been reported. Typically reported methods provide a force or pressure directly between the bend in the laminated article and the bend of a rigid support member, such as a mold or form. This presses the article bend and the bend support directly together in an attempt to inhibit the formation of wrinkles. One such method and associated apparatus is reported in U.S. Pat. No. 5,145,621--Pratt, patented Sep. 8, 1992, and assigned to the assignee of this invention. The disclosure of such patent is hereby incorporated herein by reference.